Physical, tribological and mechanical properties of polymer composite coating on silicon wafer

Silicon is an ideal material used by semiconductor industry for fabrication of micro electro mechanical systems (MEMS). But its brittleness property and hydrophilic nature has shown higher adhesion, causes higher friction and wear. It has restricted its usage in the development of MEMS. Therefore, researchers have tried to develop alternate self-lubricating material for MEMS and found a suitable epoxy polymer resin (SU-8). Hence in the current study, SU-8 is reinforced with three different fillers individually to form composite coatings and in combination to form hybrid composite coatings. Two solid fillers namely, graphite and talc and a liquid filler such as Perflouropolyether (PFPE) are used to develop the coatings. The composite and the hybrid composite coatings were deposited on plasma treated silicon wafers using a spin coating technique to obtain uniform thicknesses of similar to 100-150 micrometer. The samples were investigated to evaluate the mechanical properties (hardness and elastic modulus) using a micro hardness tester, tribological properties (friction and wear) using a nano tribometer, wettability test using a goniometer and thermal stability using a thermogravimetric analyzer. Of all the coatings, the hybrid composite coating of SU-8/talc/PFPE showed the best tribo-mechanical properties as compared to pristine SU-8. The hybrid coating showed an enhancement of similar to 4-5 times in hardness and elastic modulus and revealed a very low friction coefficient of similar to 0.05 as compared with pristine SU-8. The wettability test results showed that the surface of the SU-8 coating changed from hydrophilic to hydrophobic in nature after blending it with PFPE. Moreover, the addition of solid as well as liquid fillers in SU-8 improved the thermal stability by similar to 80-130 degrees C.